ABSTRACT 17b-hydroxysteroid dehydrogenase type 2 (17b-HSD type 2) is the central enzyme in maintaining progesterone and estrogen balance in the human endocervix during pregnancy. Data from our laboratory suggest that cervical competence during pregnancy is maintained by expression of 17b-HSD type 2 in the cervical epithelial cells resulting in inactivation of estradiol and maintenance of progesterone by to its oxidative 17b- and 20-HSD activities. During labor, however, the enzyme is down-regulated thereby increasing intracellular estradiol levels and decreasing progesterone levels, which in turn increases cervical ripening. In recent experiments, we have demonstrated that conditioned media from progestin treated cervical stroma cells dramatically increases 17b-HSD type 2 mRNA in cultured cervical epithelial cells. This observation suggests that the regulation of 17b2-HSD type 2 in the cervical epithelium is not a direct effect of progesterone, but an indirect effect, via the cervical stroma. Hence, we hypothesize that this factor, in a paracrine fashion, is involved in the regulation of 17b-HSD type 2, and perhaps other genes important for the process of cervical ripening. The long range goal of the research proposed, therefore, is to define the stromal-derived factor and to elucidate the molecular mechanism by which it regulates 17b-HSD type 2 gene expression. We speculate that dysregulation and expression of this putative paracrine factor may be a crucial component in a series of events leading to premature cervical ripening and preterm birth. The intermediate goals of this research are presented in 3 specific aims. (i) identification of progesterone- induced gene expression using DNA microarray analysis, (ii) identification of bioactive polypeptides present in conditioned media from progestin-treated stromal cells by proteomics, and (iii) assessing expression of candidate peptides/mRNAs in cervical stromal tissues and validation of efficacy of selected polypeptides using cultured cervical epithelial cells. PUBLIC HEALTH RELEVANCE: In this application, we will determine the factors produced by human cervical stromal cells in response to progesterone that mediate 17b-HSD type 2 expression in endocervical epithelial cells. The proposed studies will define an important role for stromal-epithelial interactions in mediating cervical competency during pregnancy and the mechanisms by which progesterone leads to prolongation of pregnancy in women with premature shortening of the cervix during gestation. The results will not only answer important questions regarding mechanisms in the initiation of labor, but will also provide new tools for its diagnosis thereby leading to the development of therapeutic strategies to prevent or abrogate delivery of preterm infants.